1. Field of the Invention
The present invention relates to a liquid discharge head configured to discharge a liquid.
2. Description of the Related Art
An ink jet head representative for a liquid discharge head configured to discharge a liquid can perform faster recording as the length of a discharge port array is longer. In the discharge port array, a plurality of discharge ports configured to discharge ink is arranged. For improving the recording speed, there has recently been required a full-line ink jet head having a length of discharge port array capable of recording a recording medium with more than the width of about 4 to 12 inches.
The liquid discharge head discussed in U.S. Pat. No. 6,322,206 is configured such that a plurality of liquid discharge substrates is arranged on a channel member in which channels are formed by laminating layers having openings as illustrated in FIG. 5 of U.S. Pat. No. 6,322,206. With the structure, it is possible to provide an ink jet head having a large recording width.
The liquid discharge head discussed in U.S. Pat. No. 6,322,206 is configured such that an ink inlet port and an ink outlet port are formed at both ends of the channel member in the longitudinal direction and ink is circulated inside the channels as illustrated in FIGS. 7A, 7B, and 10 of U.S. Pat. No. 6,322,206.
To cool the liquid discharge head or the like, a main channel configured to supply liquid to the liquid discharge substrates may be provided in the channel member in the direction in which the discharge ports are arranged. Since the liquid flows inside the main channel while being heated due to heat radiated from the liquid discharge substrates generated along with the discharging of the liquid, the effect of the cooling by the liquid decreases toward the downstream of the liquid flow in the main channel. As a result, the temperature of the liquid discharge substrates increases toward the downstream of the main channel.
In U.S. Pat. No. 6,322,206, an inlet port through which liquid flows, which is provided in the channel member, is provided at an end of the channel member in the longitudinal direction. However, the inlet port may be provided above the mounted face of the channel member on which the liquid discharge substrates are mounted in the vertical direction in the middle of the main channel in the liquid flowing direction. In this case, to flow the liquid from the end of the main channel in the longitudinal direction of the channel member, there may be a method that a sub-channel configured to connect the inlet port and the main channel is provided above the main channel in the channel member.
In the channel member having such a structure, the temperature of the liquid flowing through the inlet port or sub-channel is lower than the temperature of the liquid flowing through the main channel. Since the amount of liquid flowing inside the main channel decreases toward the downstream of the main channel along with the discharging of the liquid, the amount of liquid flowing through the inlet port or the sub-channel is more than the amount of liquid flowing through the main channel except for the upstream end of the main channel.
Therefore, the temperature of part of the liquid discharge substrates positioned below the mounted face of the channel member in the vertical direction in the inlet port or the sub-channel may decrease due to the effect of the cooling by the liquid in the inlet port or sub-channel. Thus, largely-affected parts and small-affected parts by the effect of the cooling of the liquid flowing through the inlet port or the sub-channel may approach each other in the liquid discharge substrates. Thus, there occurs a difference in the amount of discharged liquid due to a temperature difference of the liquid discharged in the adjacent discharge ports, which can be recognized as a difference in density on an image.